1. Field of the Invention
The present invention relates to a catalyst composition for the isomerization of n-paraffin and a process for isomerizing n-paraffin. More particularly, the present invention relates to a catalyst composition for the isomerization of n-paraffin, which comprises a specific β-zeolite as well as a process for isomerizing n-paraffin in the presence of the catalyst composition.
2. Description of the Prior Art
It is known heretofore that n-paraffin existing in a gasoline fraction is of a low octane value and is not preferable as a fuel oil for automobiles employing gasoline. On the other hand, isoparaffin, an isomer of the n-paraffin, is higher in the octane value so that it is required to increase the content of isoparaffin in gasoline. Consequently, isomerization of n-paraffin is known to be an important process for the production of gasoline. Known as an industrial scale isomerization process is a process wherein a chlorine-treated alumina carrying platinum thereon (Pt—Al2O3) is used. According to this process, however, chlorine is liberated from the catalyst and, as a result, a source of chlorine has to be supplemented at all times. Further, the liberated chlorine induces corrosion of apparatus and any trace chlorine retained in the produced oil causes a problem of environmental pollution due to chlorine. In order that a catalyst life is prolonged, it is necessary to purify the crude oil paraffin containing water, sulfur value and the like causing inactivation to have a concentration of 1 ppm or lower. For these reasons, there is a great demand of developing a clean isomerization process. Crystalline aluminosilicates (zeolite), zirconia sulfate, molybdenum trioxide, etc. are known heretofore as a catalyst for the isomerization of n-paraffin lower in environmental load. Among the crystalline aluminosilicates, β-zeolite is known to exhibit a high degree of isomerization activity.
β-Zeolite is an aluminosilicate comprised of three-dimensional 12-oxygen membered-ring micropores, and its crystalline structure and chemical composition are disclosed in Atlas of Zeolite Framework Type s, 5th Revised Edition 2001, Ch, Baerlocher, W. M. Meier, D. H. Olson, 2001, Elsevier. As to the process for preparing β-zeolite, it is disclosed in various literatures, for example, U.S. Pat. No. 3,308,069; U.S. Pat. No. 4,642,226; Japanese Laid-open Patent Appln. No. Hei. 5-201722; Japanese Laid-open Patent Appln. No. Hei. 6-91174; Japanese Published Patent Appln. No. 8-509452; etc. In addition, a synthetic method of β-zeolite according to the so-called dry gel process is disclosed in Topics in Catalysis, 9, 1441 (1999).
β-Zeolite is excellent in isomerizing ability of n-paraffin but has such a drawback that a rapid deterioration in the activity takes place within a short period of time on account of precipitation of a large amount of carbon, thus shortening the catalyst life. The use of a zeolite carrying a noble metal thereon is adopted as a means for inhibiting reduction of the catalytic activity. For suppressing the reduction of the catalytic activity completely, however, it is necessary to inhibit the inherent ability of the catalyst for precipitation of carbon. Hence, there is a great demand for developing a novel catalyst capable of decreasing the precipitation of carbon on isomerization of n-paraffin.